Unique behaviour of the α-helix in bending deformation.

The maximum degree of bending that can be tolerated by the rigid rod-like α-helix remains unknown; however, it should be very difficult or even impossible to make α-helices with varying degrees of curvature in folded proteins. As an experimentally tractable model, here we utilize cyclic proteins and peptides to determine the maximum possible bending in the α-helix. We artificially enforced bending in the α-helices by using variously sized macrocycles and compared the structural characteristics of the macrocycles with those of their linear counterparts. This differential analysis reveals that the radius of curvature (RC) for the maximally bent α-helix is approximately 10 times smaller than those of typical α-helices found in natural proteins. Together with the novel finding of the limit of α-helix deformation, excessively bent α-helices can be further utilized in designing de novo peptides and proteins with unique structures and peculiar functions.